Breath testing system with increased sensitivity

ABSTRACT

Increased sensitivity to alcohol content of a subject&#39;&#39;s breath is obtained in a catalytic oxidation or combustion detector by flowing a breath sample through a heated chamber containing a maze of substrate elements, such as fibrous glass wool, coated with a catalytic material and providing a total catalytic surface area which is very large compared to the mass of the substrate elements. The alcohol constituent oxidizes as the molecules contact the catalytic material, and as a result of the oxidation reaction the temperature increases in an amount directly proportional not only to the alcohol concentration but also to the catalytic area/mass ratio. A temperature-sensing device, such as a thermistor, responds to the temperature change and effects the development of an output information signal, the amplitude of which accurately represents the breath alcohol concentration.

United StatesPatent [19 1 Venema v[ June 25, 1974 [54] gg ggg s' 2 3 W FOREIGN PATENTS 0R APPLICATIONS 464,798 4/1937 Great Britain 340/237 R [75] Inventor: Harry J. Venema, Wheaton, Ill.

- Primary Examiner-Kyle L. Howell 73 l Asslgnee gfi Warner Corporatmn Chicago Attorney. Agent, or Firm-Donald W. Banner [22] Filed: July 3, 1972 [57] ABSTRACT [211 App], NO 268,340 Increased sensitivity to alcohol content of a subjects breath is obtained in a catalytic oxidation or combustion detector by flowing a breath sample through a [52] 128/2 23/255 73/27 heated chamber containing a maze of substrate ele- 340/237 R ments, such as fibrous glass wool, coated with a catat i l d p idi g a t t l t lyti Surface [58] Fletld Search 'fl' 2 area which is very large compared to the mass of the 73/27 R; 23/232 E1 254 255 E; 340/237 substrate elements. The alcohol constituent oxidizes as the molecules contact the catalytic material, and as a References cued result of the oxidation reaction the temperature in UNITED STATES PATENTS creases in an amount directly proportional not only to 1,992,747 2/1935 Gilliland et al. 340/237 R the alcohol concentration but also to the catalytic 2,114,401 4/1938 Price 340/237 R area/mass ratio. A temperature-sensing device, such as 2 .128 /194! Miller 23/232 E a thermistor, responds to the temperature change and 2,244,366 J3, CObSOH et 3| E effects the development of an utput information ig nal, the amplitude of which accurately represents the TOWN 6 a 3,239,828 3/1966 Peterman 340/237 R breath alcohol concentrat'on' 3,600,!34 8/1971 BREATH RECEIVING AePARA-rus 'Nollei. 23/232-E v ALCOHOL DETECTOR l3\l 1 Claim, 1 Drawing Figure OUTPUT UTlLlZlNG APPARATUS 1 a BREATH TESTING SYSTEM WITH INCREASED SENSITIVITY BACKGROUND OF, THE INVENTION Various breath testing systems have been developed for evaluating a persons breath to detect its alcohol level. In one well known system, a sample of the breath to be analyzed ispassed over a heated catalyst resistance element where any alcohol present in the breath sample oxidizes. The heat of the oxidation reaction causes the temperature and consequently the resistance of the catalytic element to increase, and this in turn causes an output information signal to be produced which indicates the particular alcohol level in the breath sampled. Usually, the catalytic element forms one leg of a normally-balanced wheatstone bridge which unbalances, when the resistance of that element changes as a result of oxidation of breath alcohol, the degree of unbalance being proportional to the alcohol concentration. In its simplest form, the heated catalyst resistance element is a platinum wire which constitutes a catalyst as well as a thermistor, namely a resistor whose resistance varies with temperature. The required heating is accomplished by constantly flowing quiescent or steadystate current through the platinum wire. The molecules of the breath sample must come incontact with the platinum wire to react and cause the temperature of the wire to increase. However, since the surface area of the wire is relatively small, a small number of molecules will contact it. The temperature and resistance of the wire will therefore increase very little in the presence of alcohol, resulting in an alcohol detector of low sensitivity. In many cases the detector includes a combination heater-thermistor element around which is wrapped a head or sleeve formed of some catalytic material. The surface area of the bead is much larger than that of the platinum wire so that considerably greater contact will be made with the molecules of the breath sample, anda greatertemperature and resistance increase will occur for a given alcohol concentration as compared to the case of the-platinum wire.

Of course, the greater the temperature change in re.-

sponse to a given alcohol concentration, the greater.

willbe the detectors sensitivity and the more accurate the test results. Hence, it is most desirable to maximize teristic that varies with temperature changes in the chamber. There is also located within the chamber an alcohol-oxidizing means which includes a maze of substrate elements each coated with a catalytic material to obtain a relatively'high ratio of total catalytic surface area to total mass or weight. This will maximize the number of molecules, of any gas sample passed through the maze, that will come in contact withthe catalytic material. Breath receiving apparatus provides a sample of breath received from a person to be tested. There are means for supplying the breath sample to the heated chamber and through the maze where any alcohol present in the sample oxidizes. The oxidation reaction releases thermal energy to increase the tempera- DESCRIPTION OF THE DRAWING The features of the invention which are believed to be novel are set forth with-particularity in the appended claims. The invention, together with further advantages and features thereof, may best be understood, however, by reference to the followingdescription in conjunction with the accompanying drawing, the single the catalytic surface area contacting the molecules of SUMMARY OF THE INVENTION The breath testing system of the invention determines the breath alcohol concentration of a person and comprises means for providing a heated chamber, within which is disposed a temperature-sensing device, such as a thermistor, having a predetermined charac- FIGURE of which is a diagram,partly in block form and partly in schematic, of a breathtesting system constructed in accordance with one embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Breath receiving apparatus 10 develops a measured sample of breath received from a subject under test. The apparatus may takeany suitable construction to facilitate the receipt of breath blown or exhaled by the person and to deliver a sample of that breath to the outlet of the apparatus, theunused breath being vented or dumped to the atmosphere. One example of an appropriate form for apparatus 10 is found in copending application Ser. No. 136,778, filed Apr. 23, 1971 the names of Donald W. Collier, Joseph P. Hoppesch and Anthony C. Mamo, and issued Oct. 9, 1973 as US. Pat. No. 3,764,270.

While not essential for the proper operation of the present invention, apparatus 10 preferably includes appropriate control equipment to make certain that the breath sample constitutes deep lung breath. Suitable control equipment to perform that function is also illustrated and described in the aforementioned copending application Ser. No. 136,778. There, a breath sample is not produced at the outlet of the breath receiving apparatus until a continuous uninterrupted breath flow has occurred for a predetermined time period, such as 5 seconds. A sample taken at the end of a 5-second interval of uninterrupted blowing or exhaling constitutes deep lung breath, from which an accurate reading of alcohol level may be obtained as is well known in the art.

The alcohol concentration in the deep lung breath sampled is determined by an alcohol detector 13 which develops an electrical information signal, the amplitude of which reflects the breath alcohol level. More particularly, each breath sample from apparatus is channeled to one end of a tubular or cylindrical shaped enclosure 15, made for example of glass or plastic, the other end of which opens to the atmosphere. A flat sep arating wall 16, which may also be constructed of glass or plastic, divides cylindrical tube into two halves to provide two chambers 17, 18 of equal volume. With this construction, a breath sample emanating at the outlet of apparatus 10 is split by wall 16 into two equal portions, one of which flows through chamber 17 and then to the atmosphere via the open end of tube 15, while the other portion simultaneously flows through chamber 18 and thence to the atmosphere.

Each chamber, which is heated in a manner to be explained, contains a temperature-sensing device for measuring or recording the temperature within the chamber. These devices, labeled 21 and 22, have predetermined characteristics or properties that vary with temperature. Preferably, devices 21 and 22 are identical thermistors whose resistances vary in response to temperature variations.

Thermistors 21 and 22 are included in and form part of a normally-balanced, four-legged wheatstone bridge. Specifically, thermistors 21 and 22 constitute respective ones of two adjacent legs of the bridge circuit. A pair of simple, equal size resistors 25 and 26 function as the other two adjacent legs. Bridge junction 27 connects to the positive terminal 28 of a source of DC. operating potential, while junction 29 is connected to the negative terminal 31 of that potential source. Direct current therefore flows continuously from positive terminal 28 to negative terminal 31 through two parallel paths one provided by legs 21 and 22 and the other by legs 25 and 26. The constant current flow through devices 21 and 22 produces heat to heat chambers 17 and 18. Preferably, however, the required heating of chambers 17 and 18 is accomplished by a separate cylindrical shaped heater 34 which forms a jacket around the outside of tube 15. Heater 34 may, for example, be a heating coil through which current passes.

Since thermistors 21 and 22 normally have the same resistance and, since resistors 25 and 26 are of equal electrical size, in the absence of any external stimulation the bridge circuit will be balanced and junctions 32 and .33 will be established at identical voltage levels. The output of alcohol detector 13 is derived between junctions 33 and 32 and with a zero voltage difference existing between those junctions no output signal will be developed by alcohol detector 13. The output signal will also have zero amplitude when a breath sample, containing no alcohol, is delivered to heated chambers 17 and 18 from apparatus 10. The alcohol-free breath will flow through those chambers and to the atmosphere without causing any chemical reaction and/or temperature change. Detector 13 will be unresponsive to the breath sample.

In accordance with the present invention, a very small amount of breath alcohol will upset or unbalance the bridge circuit to produce an output signal having a finite amplitude precisely representing the alcohol concentration. In other words, alcohol detector 13 is extremely sensitive to the presence of breath alcohol and a very small change in alcohol concentration results in a measurable change in the amplitude of the output signal to provide a read-out which accurately depicts the alcohol level. This is accomplished by causing the temperature in chamber 17 to vary to a substantial extent in response to the slightest change in breath alcohol concentration.

More particularly, a maze or bulk of substrate elements, preferably formed of glass wool fibers, is included in each of chambers 17 and 18. Of course, the fibers are sufficiently loosely packed into each chamber to pennit breath flow through the entire length of tube 15. Each of the substrate elements or fibers of the maze (labeled 35) in chamber 17 is coated with a catalytic material, while the maze 36 of substrate elements in chamber 18 remains uncoated. Hence, maze 35 serves as an alcohol-oxidizing means since any alcohol in the breath sample flowing through chamber 17 oxidizes as it contacts the catalytic material. By employing the maze 35 of catalyst-coated substrate elements, there is obtained a total catalytic surface area which is very large compared to the mass or weight of the substrate elements. This will maximize the number of molecules coming in contact with the catalytic material so that the thermal energy released by the oxidation reaction effects a substantial temperature increase within chamber 17 even in response to low alcohol concentrations. This follows inasmuch as the temperature change will vary in direct proportion to the catalytic area/mass ratio as well as in direct proportion to the alcohol concentration. Preferably, the catalyst coated substrate elements should also have a thermal capacitance as low as possible since the temperature increase is inversely proportional to the thermal capacitance.

Temperature-sensing device 21 increases in resistance in response to the temperature increase and to an extent directly proportional to the alcohol level. Meanwhile, the non-catalytic maze 36 in chamber 18 is unresponsive to the alcohol in' the breath flowing through that chamber and thus the resistance of device 22 remains unchanged. With unequal resistances for thermistors 21 and 22, the bridge circuit becomes unbalanced as the voltage drops in those thermistors will be unequal and this causes junction 32 to be established at a voltage different than that at junction 33. The magnitude of the differential represents the degree of unbalance and the particular alcohol level in the breath sampled. The output information signal, produced between junctions 33 and 32 and applied to output utilizing apparatus 39, therefore has an amplitude directly proportional to and representing the breath alcohol concentration.

Output utilizing apparatus 39 may include a meter which effectively measures the information signal amplitude, thereby providing a visual display of the alcohol concentration in the tested breath sample. Alternatively, the output apparatus can be a simple bulb energized when the infonnation signal exceeds a predetermined threshold amplitude level.

Apparatus 39 maytake any of a variety of different fonns inasmuch as there are many devices that can be controlled by an electrical signal whose amplitude signifies the alcohol level of a persons breath.

Of course, an amplifier may be interposed between alcohol detector 13 and apparatus 39 so that the information signal may be amplified before it is applied to the output utilizing apparatus. No amplifier is illustrated in order to simplify the drawing as much as possible.

It is to be understood that the invention need not be embodied in a bridge type alcohol detector, but may be incorporated in any alcohol detector of the type having acatalyst which oxidizes breath alcohol and produces a temperature changeto in turn effect the development of an output information signal reflecting the alcohol content. For example, the detector may merely comprise a single thermistor through which direct current continuously flows and around which a breath sample flows through amaze of catalyst coated substrate elements to produce an oxidation reaction to vary the temperature of the thermistor thereby varying the current therethrough. The detector's output signal would be determined by the current flowing through the thermistor.

Of course, in the illustrated embodiment the advantages of the present invention are combined with those achieved in a conventional bridge type detector. For example, since the adjacent legs provided by devices 21 and 22 are (with the sole exception of the catalytic material in chamber 35) located in identical environments, are identical in construction and are simultaneously exposed to the same breath sample, any change in either one of those legs caused by thermoconductivity, convection, etc., will be balanced out by an equal and compensating change in the other leg. In addition, current changes due to power supply variations are also cancelled out. if desired, the invention could be incorporated in an AC bridge rather than the DC bridge illustrated.

The invention provides, therefore, an improved breath alcohol detection system of the catalytic oxidation or combustion type that achieves a substantially greater sensitivity to alcohol content than previously possible in similar type breath analyzers. This is accomplished by utilizing a maze of catalyst covered substrate elements to increase the area contact between the gas molecules and the catalyst.

While a particular embodiment of the invention has been shown and described, modifications may be 6 made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

1 claim: 1. A breath testing system for determining the breath alcohol concentration of a person, comprising:

means for providing a heated chamber; a temperature-sensing device within said chamber and having a predetermined characteristic which varies with temperature changes in said chamber;

alcohol-oxidizing means within said chamber and including a maze of substrate elements, formed of glass wool fibers having a relatively low thermal capacitance, each of which elements is coated with a catalytic material to obtain a relatively high ratio of total catalytic surface area to total mass and to maximize the number of molecules, of any gas sample passed through said maze, that will come in contact with the catalytic material;

breath receiving apparatus for providing a sample of breath received from a person to be tested;

means for supplying said breath sample to said heated chamber and through said maze where any alcohol present in said breath sample oxidizes, the oxidation reaction releasing thermal energy to increase'the temperature in said chamber in direct proportion to the alcohol concentration in said breath sample and in direct proportion to said ratio, said maze thereby effectively increasing the sensitivity of said alcohol-oxidizing means to breath alcohol;

and means, coupled to and controlled by said temperature-sensing device, for developing an output information signal having an amplitude directly proportional, to the alcohol concentration in said breath sample. 

1. A breath testing system for determining the breath alcohol concentration of a person, comprising: means for providing a heated chamber; a temperature-sensing device within said chamber and having a predetermined characteristic which varies with temperature changes in said chamber; alcohol-oxidizing means within said chamber and including a maze of substrate elements, formed of glass wool fibers having a relatively low thermal capacitance, each of which elements is coated with a catalytic material to obtain a relatively high ratio of total catalytic surface area to total mass and to maximize the number of molecules, of any gas sample passed through said maze, that will come in contact with the catalytic material; breath receiving apparatus for providing a sample of breath received from a person to be tested; means for supplying said breath sample to said heated chamber and through said maze where any alcohol present in said breath sample oxidizes, the oxidation reaction releasing thermal energy to increase the temperature in said chamber in direct proportion to the alcohol concentration in said breath sample and in direct proportion to said ratio, said maze thereby effectively increasing the sensitivity of said alcoholoxidizing means to breath alcohol; and means, coupled to and controlled by said temperature-sensing device, for developing an output information signal having an amplitude directly proportional to the alcohol concentration in said breath sample. 